At the beginning of the series, prisoners in Azkaban are guarded by Dementors, creatures that feed on positive emotions. This means that prisoners eventually lose all hope and good feelings and thoughts. They are forced by the Dementors to relive the darkest, most terrible experiences of their lives over and over again. Most prisoners of Azkaban are driven mad, while others just die of despair.
During Voldemort's return to power, the Dementors allowed the escape of a large number of Death Eaters, Voldemort's minions. They eventually deserted Azkaban and joined Voldemort, leaving the prison guardless. After Voldemort's defeat, new Minister for Magic Kingsley Shacklebolt made sure that Dementors would have no part in guarding Azkaban. While this caused the place to become a bit more cheerful, it probably prevented a number of problems as well.
- Black, Sirius
- was sent to Azkaban without trial for the betrayal of Lily and James Potter to Voldemort and for killing Peter Pettigrew. Both of these charges were later proved false.
- Crouch, Jr., Bartemius "Barty"
- was sent to Azkaban for participating in the torture of Frank and Alice Longbottom. He escaped disguised as his mother, who died in his place a year later and was buried under his name.
- Dumbledore, Percival
- was sent to Azkaban for attacking three Muggle children after their attack on his daughter.
- Hagrid, Rubeus
- was sent to Azkaban without trial for setting a basilisk on students at Hogwarts. He was proven innocent and set free a few weeks later.
- Lestrange, Bellatrix
- was a Death Eater sent to Azkaban for participating in the torture of the Longbottoms. She later escaped in the mass breakout.
- Malfoy, Lucius
- was a Death Eater captured at the battle at the Department of Mysteries. He later escaped in the mass breakout.